A highly-integrated optical phase-locked loop with a phase/frequency detector and a single-sideband mixer (SSBM) has been proposed and demonstrated for the first time. A photonic integrated circuit (PIC) has been designed, fabricated and tested, together with an electronic IC (EIC). The PIC integrates a widely-tunable sampled-grating distributed-Bragg-reflector laser, an optical 90 degree hybrid and four high-speed photodetectors on the InGaAsP/InP platform. The EIC adds a single-sideband mixer, and a digital phase/frequency detector, to provide single-sideband heterodyne locking from -9 GHz to 7.5 GHz. The loop bandwith is 400 MHz.

No abstract

While gallium nitride (GaN) is attracting broad attention as the wide bandgap material of choice for both industrial and defense applications, thermal impediments present a significant barrier to full exploitation of its inherently high electron sheet charge density and electrical breakdown voltage. For the last four years, the Defense Advanced Research Projects Agency (DARPA) has pursued research focused on reduction of near-junction thermal resistance through use of diamond substrates and convective and evaporative microfluidics. The options, challenges, and techniques associated with the development of this embedded thermal management technology are described, with emphasis on the accomplishments and status of efforts related to GaN power am plifiers.

No abstract

GaN has emerged as the material of choice for advanced power amplifier devices for both industrial and defense applications but near-junction thermal barriers severely limit the inherent capability of high-quality GaN materials. Recent “embedded cooling” efforts, funded by Defense Advanced Research Projects Agency Microsystems Technology Office (DARPA-MTO), have focused on reduction of this near-junction thermal resistance, through the use of diamond substrates and efficient removal of the dissipated power with convective and evaporative microfluidics. An overview of the accomplishments of the DARPA Near-Junction Thermal Transport (NJTT) program and recent results from the on-going DARPA Intra-Chip Embedded Cooling (ICECool) program are provided. It is shown that growth or bonding of diamond to GaN epitaxy has enabled a 3-5× increase in power handling capability per transistor unit area, while use of microfluidic cooling has enabled heat fluxes of 30 kW/cm2at the transistor level and 1 kW/cm2at the die-level, for a 3-6× improvement in the total RF output power of GaN power amplifiers. These demonstrations provide near-term validation of the large improvement in output power gained through embedded cooling and confirm the potential for well above a 6× improvement in GaN power amplifier output power to the electrical, rather than thermal, limits of GaN.